What is lignite and why is it particularly carbon-intensive when burned?

• A. Lignite is a high-rank coal with low moisture content; it has high energy density.
• B. Lignite is a low-rank coal with high moisture content; it has lower energy density and higher emissions per unit energy due to moisture and impurities.
• C. Lignite is a natural gas disguised as coal.
• D. Lignite is a synthetic coal produced in laboratories with minimal emissions.

Answer: (B)

Lignite is a low-rank coal with high moisture content. That means a large portion of its mass is water that must be heated and boiled away during combustion. Because of this, the energy you get from burning lignite per kilogram is much lower than for higher-rank coals, so you need to burn more of it to get the same amount of heat or electricity.

The moisture issue also means more fuel is consumed to deliver the same energy, which translates into more carbon dioxide released overall for the same energy output. In addition, lignite tends to have more impurities and a lower carbon concentration per kilogram, which further reduces efficiency and raises emissions per unit of energy. All of this makes lignite particularly carbon-intensive when burned.

In short, lignite is a low-rank coal with high moisture, giving it low energy density and higher emissions per unit energy due to the energy demand of evaporating water and other impurities.